I want to play a certain stage, or at least restart the "campaign". When I go for New Game, it says it will reset my profile. I don't want to lose my weapon upgrades or parts. I'd just like to repeat the earlier stages to go for no repair kit achievements and whatnot.

So if I go for New Game, will it get rid of my weapon upgrades and parts? How can I select a stage and repeat however many times I want without having to loop the entire story?